The present invention relates in general to vibration damped blades for turbo-machinery. More particularly, the present invention relates to vibration damped fan and compressor blades for such turbo machinery, which blades include a metallic substrate and a vibration damping coating bonding with a surface of the metallic substrate and defining an exterior surface for the blades.
Turbo-machinery such as combustion turbine engines and air cycle machines include high-speed turbine wheels, compressor wheels, and fans that expand, compress, and move ambient air or other working fluids. Blades of the wheels and fans frequently encounter vibrations. The vibrations can affect fatigue life of the blades and, consequently, shorten the useful life of the blades.
U.S. Pat. No.3,301,530 to W. R. Lull and U.S. Pat. No.3,758,233 to Cross et al. both show vibration damping coatings applied to turbo-machine blades. The blades and coatings shown in the Lull and Cross et. al. patents both carry coatings of more than one layer. The Lull patent shows intermediate and overlying outer sub-layers that are both made of metals having differing coefficients of elasticity. Similarly, the Cross et. al. patent shows coating sub-layers that are selected from a ceramic, and from a mixture of the selected ceramic along with the metal from which the turbo-machine blade itself is formed.
Such damped blades and vibration damping coatings utilizing plural sub-layers can be both expensive and difficult to manufacture. Particularly, the vibration damping coatings can be difficult to apply successfully. Because of the necessity to control such factors as the thicknesses of the sub-layers, the interbonding of the sub-layers with the substrate of the blade and with one another, and other manufacturing parameters, the opportunities for error in the manufacture of such vibration damped blades is increased, and the opportunities for variability in the manufacturing process are multiplied. The differing materials of the sub-layers shown in the Lull and Cross et al. patents are likely to have differing coefficients of thermal expansion that may lead to separation of these layers during manufacturing or during use of the blade. Thus, manufacturing costs for vibration damped blades utilizing the known technology may be high, and scrap and error rates may also be excessive.